Aqueous air foam

ABSTRACT

An aqueous air foam comprising a non-crosslinked cellulose ether selected from C 1 -C 3 -alkyl celluloses, C 1 -C 3 -alkyl hydroxy-C 1-3 -alkyl celluloses, hydroxy-C 1-3 -alkyl celluloses, or mixed hydroxy-C 1 -C 3 -alkyl celluloses, the foam having a foam quality FQ of from 60 to 97 percent and the foam quality being defined as FQ(%)=[air volume/(air volume+fluid volume)×100].

[0001] The present invention relates to aqueous air foam and to the useof such air foam.

BACKGROUND OF THE INVENTION

[0002] Aqueous foams are generally known.

[0003] U.S. Pat. No. 4,683,004 discloses foamable compositions and theiruse as hair styling mousses and foaming hand lotions and cleansers. Thefoamable composition comprises water and a foam stabilizer. The foamstabilizer is a non-ionic cellulose ether which is substituted withmethyl, hydroxyethyl or hydroxypropyl groups and which further issubstituted with a long chain alkyl radical having 10 to 24 carbonatoms. The foamable composition comprises a hydrocarbon propellant.

[0004] European patent application EP-A-0 362 655 discloses foamablepharmaceutical compositions which comprise water, a gel forming agent,an effective amount of a drug and a propellant. The gel forming agentpreferably is a water-soluble cellulose derivative, such asmethylcellulose, or gelatin. The propellant is preferably carbon dioxideand nitrous oxide.

[0005] For easy availability of the gas and for environmental reasons,it is desirable to provide aqueous air foams which are useful forvarious applications, that means foams which are made by physicallymixing air into a fluid.

[0006] U.S. Pat. No. 5,026,735 relates to the treatment of hazardousmaterial or other substrate with aqueous air foam. The foam is producedfrom a water-based composition which comprises (a) a water-solublepolyhydroxy polymer, such as guar gum or poly(vinyl alcohol), (b) apolyvalent ionic complexing agent, such as borax, (c) a foaming agent,such as various surfactants, (d) a pH modifier, and (e) water as themain component.

[0007] One object of the present invention is to provide new aqueous airfoam which is suitable for various uses, such as powder granulation orcoating solid particles like tablets.

SUMMARY OF THE INVENTION

[0008] One aspect of the present invention is an aqueous air foam whichcomprises a non-crosslinked cellulose ether selected from C₁-C₃-alkylcelluloses, C₁-C₃-alkyl hydroxy-C₁₋₃-alkyl celluloses,hydroxy-C₁₋₃-alkyl celluloses or mixed hydroxy-C₁-C₃-alkyl celluloses,wherein the foam has a foam quality FQ of from 60 to 97 percent and thefoam quality is defined as FQ(%)=[air volume/(air volume+fluidvolume)×100].

[0009] Another aspect of the present invention is the use of theabove-mentioned foam for agglomerating solid particles.

[0010] Yet another aspect of the present invention is the use of theabove-mentioned foam for coating solid particles.

[0011] Yet another aspect of the present invention is a process foragglomerating solid particles wherein the above-mentioned foam iscontacted with the solid particles to be agglomerated.

[0012] Yet another aspect of the present invention is a process forcoating solid particles wherein the above-mentioned foam is contactedwith the solid particles to be coated.

SHORT DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 illustrates a foam-generating device for producing the foamof the present invention.

[0014]FIG. 2 represents a photograph of foam flowing through a tube ofthe foam-generating device illustrated in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The foam of the present invention is an air aqueous foam. Thismeans that more than 50 weight percent, preferably at least 60 weightpercent, more preferably at least 75 weight percent and most preferablyat least 95 weight percent of the liquid comprised in the foam is water.The term “air foam” is used in its industry-accepted sense to mean afoam made by physically mixing air into a fluid, and thus the term isdistinct from chemical or carbon dioxide foam or halocarbon blown foam.The foam may contain a minor amount of a gas other than air, such ascarbon dioxide, or a hydrocarbon or halocarbon that is gaseous at roomtemperature and atmospheric pressure. However the air should amount toat least 70 percent, preferably at least 80 percent, more preferably atleast 95 percent of the entire gas volume. Most preferably, the foamdoes not contain another gas than air.

[0016] The foam of the present invention comprises a non-crosslinkedcellulose ether selected from C₁-C₃-alkyl celluloses, such asmethylcelluloses; C₁-C₃-alkyl hydroxy-C₁₋₃-alkyl celluloses, such ashydroxyethyl methylcelluloses, hydroxypropyl methylcelluloses or ethylhydroxyethyl celluloses; hydroxy-C₁₋₃-alkyl celluloses, such ashydroxyethyl celluloses or hydroxypropyl celluloses; or mixedhydroxy-C₁-C₃-alkyl celluloses, such as hydroxyethyl hydroxypropylcelluloses. Preferably, water-soluble cellulose ethers are comprised inthe foam. More preferably, the foam comprises a methylcellulose or ahydroxypropyl methylcellulose. Most preferably, the foam comprises amethylcellulose with a methyl molar substitution DS_(methoxyl) of from0.5 to 3.0, preferably from 1 to 2.5, or a hydroxypropyl methylcellulosewith a DS_(methoxyl) of from 0.5 to 3.0, preferably from 1 to 2.5 and aMS_(hydroxypropoxyl) of from 0.05 to 2.0, preferably from 0.1 to 1.5.The viscosity of the cellulose ether preferably is from 1 to 100,000mPa·s, more preferably from 3 to 10,000 mPa·s, most preferably from 5 to5,000 mPa·s, measured as a 2-wt. % aqueous solution at 20° C. using anUbbelohde viscometer.

[0017] The aqueous air foam generally comprises from 0.01 to 30 percent,preferably from 0.1 to 20 percent, more preferably from 0.5 to 15percent, and most preferably from 1 to 5 percent of the non-crosslinkedcellulose ether and from 99.99 to 70 percent, preferably from 99.9 to 80percent, more preferably from 99.5 to 85 percent, and most preferablyfrom 99 to 95 percent of water, based on the total weight of thecellulose ether and water.

[0018] Preferably, the foam does not comprise a substantial amount of asurfactant other than the cellulose ether. This means that an aqueousfluid composition which comprises an above-mentioned cellulose ether andwhich is used for preparing the foam of the present invention preferablydoes not contain a surfactant other than the cellulose ether in asufficient amount to cause foaming of the fluid composition upon contactwith air. More preferably, the fluid composition does not comprise anyamount of a surfactant other than the cellulose ether. Most preferably,the fluid composition does not comprise a known nonionic, cationic,anionic or amphoteric surfactant, as for example listed in U.S. Pat. No.5,026,735, column 6, lines 47-68 and column 7, lines 1-22.

[0019] The foam may contain one or more additional solid or liquidcomponents such as drugs, fillers, pigments flavors or plasticizers. Ifpresent, their total amount is generally up to 75 percent, preferably upto 50 percent, more preferably up to 25 percent, based on the totalweight of the foam. A two-phase foam is composed of an aqueous phase anda gaseous phase. A three-phase foam may comprise, in addition to aqueousand gaseous phases, insoluble solids or immiscible liquids. Suchthree-phase foams can also contain dissolved solids in the aqueous orimmiscible liquid phase or in both liquid phases. Four-phase foams maycomprise, in addition to aqueous and gaseous phases, immiscible liquidsand insoluble solids. In all foams, any immiscible liquid phase may bepresent as an oil-in-water or water-in-oil emulsion or as a simpledispersion.

[0020] For producing the foam of the present invention a fluidcomposition comprising water, one or more of the above-mentionedcellulose ethers and optionally one or more of the above-mentionedadditives is contacted with air to produce a foam. The foam can beproduced in a known manner by mechanically or physically entraining ordispersing the air in the fluid composition, for example by pumping thefluid composition to air-aspirating, foam producing equipment. Oneuseful and simple foam generating device is shown in FIG. 1.

[0021] The produced foam comprises a discontinuous air phase, and acontinuous aqueous phase, comprising the polymer and bound liquid.Generally the lamella or fluid film of the air bubbles is viscous due tothe presence of the polymer. Water is retained in the lamella of the airbubbles. The drainage of the liquid from the lamellae is minimized,reduced or prevented; such foam is designated as “non-draining foam” inthe art.

[0022] The foam of the present invention generally has an average bubblediameter in the range of from about 1 micrometer to about 2,000micrometers, preferably from about 5 micrometers to about 1,000micrometers, more preferably from about 10 micrometers to about 300micrometers. It is to be understood that the measurements of the foamdiameter generally are not very accurate in view of the dynamicproperties of the foam.

[0023] The foam preferably has a measured density of up to 0.1 g/cm³.

[0024] It has been found that the foam of the present invention has asurprisingly high foam quality. The foam quality FQ is given in percentat atmospheric pressure and 25° C. and is defined as follows:

FQ(%)=[gas volume/(gas volume+fluid volume)×100].

[0025] The foam quality can be measured by measuring the foam volumethat is produced from a given volume of fluid at atmospheric pressureand 25° C. The foams of the present invention have a foam quality offrom 60 to 97 percent, preferably from 65 to 95 percent, ore preferablyfrom 75 to 95 percent. Such high foam quality is surprising fornon-raining foams. The foam quality FQ as defined herein is the measuredfoam quality.

[0026] It has been observed that the above-mentioned measured foamquality FQ is surprisingly close to the theoretical foam quality FQ_(T).

FQ _(T) =[V supplied gas/(V supplied gas+V supplied fluid)×100],

[0027] wherein V means the volume at 25° C. and atmospheric pressurethat is supplied per time unit during the foam production, for examplethe supplied volume per minute. It goes without saying that the sametime unit has to be taken for the supplied volume of gas and thesupplied volume of fluid to calculate FQ_(T).

[0028] Surprisingly, is has been found that the theoretical foam qualityFQ_(T) is generally only up to 1.75 times as high, in many cases evenonly up to 1.5 times as high, and in the most preferred embodiments ofthe invention only up to 1.2 times as high as the measured foam qualityFQ. Such a high measured foam quality is highly desirable. The lowliquid content in the foam reduces the time which is necessary fordrying the foam after its use, for example for drying powder which hasbeen agglomerated with the foam or for drying particles which have beencoated with the foam of the present invention.

[0029] It has surprisingly been found that foams can be produced whichare useful in various applications, such as granulating solid particleslike powders or coating solid particles like tablets, even when thevolume of the supplied gas is very large, as compared to the volume ofthe supplied liquid in a foam generating device. For example, gases witha theoretical foam quality FQ_(T) as high as 99.8 percent have shown togive excellent results in powder granulation trials. As indicated above,the aqueous air foam of the invention comprising non-crosslinkedcellulose ether is a non-draining foam. Skilled artisans expect fornon-draining foams the formation of a mist, this means the formation ofliquid droplets in air, when the theoretical foam quality FQ_(T) isabout 96 percent or higher. In known non-draining foams with atheoretical foam quality FQ_(T) of about 96 percent or more, the foambubbles deform from spherical to multihedral to increase the packingefficiency of the bubbles. The foam bubbles may only deform bydisplacing liquid from the lamellae. The displaced liquid eventuallyforms liquid droplets in air.

[0030] Surprisingly, it has been found that useful foams can be producedwith a higher supplied and measured air/water ratio, that means a highermeasured foam quality FQ, than can be expected for non-draining foamswith spherical bubbles. Generally the foams of the present invention canhave a theoretical foam quality FQ_(T) of from 65 to 99.9 percent,preferably of from 75 to 99.8 percent, more preferably from 85 to 99.8percent. Even at a theoretical foam quality FQ_(T) of more than 96percent, the formation of a mist has not been observed. Without wantingto be bound to the theory, it is believed that this unexpectedly highfoam quality that can be achieved in the foam of the present inventionis due to pockets of air which are entrapped in pockets of foam. Pocketsof foam interspersed with pockets of air have been observed in foams ofthe present invention. FIG. 2 represents a photograph of foam of thepresent invention flowing through a tube of a foam-generating device.Air-foam boundaries are visible, which indicates that pockets of foamare interspersed with pockets of air.

[0031] It has been found that one way of producing foam of a highermeasured foam quality FQ is the production of the foam in a foamgenerating device under pressure by contacting a stream of theabove-described fluid composition comprising water, one or more of theabove-mentioned cellulose ethers and optionally one or more of theabove-mentioned additives with a stream of air and to release theproduced foam to ambient pressure. The pressure of the aqueous fluidstream preferably is from 135 to 1,100 kPa, more preferably from 350 to700 kPa, most preferably about 414 kPa. The pressure of the air streamis preferably from 13 to 70 kPa lower, more preferably from 20 to 50 kPalower, most preferably from 25 to 40 kPa lower than the pressure of theaqueous fluid stream. When the foam is released from the foam generatingdevice operating under pressure, the foam expels excess air to maintainits foam structure. Expelled air forms pockets of air within the foam.

[0032] The foam of the present invention is useful for agglomeratingsolid particles, such as a powder. The particles can be of any shape,such as spherical, elliptic, or fibrous. The solid particles generallyhas an average particle size of less than 2500 micrometers, preferablyless than 1000 micrometers, more preferably less than 750 micrometers,most preferably less than 500 micrometers. The foam of the presentinvention is particularly useful for agglomerating powders. Therefore,the following description refers to powders although the agglomerationprocess is not limited to powders. The weight ratio between the foam andthe powder generally is from 1:20 to 1:0.2, preferably from 1:10 to1:0.5, more preferably from 1:5 to 1:1. Preferably, the foam and thepowder are contacted in such ratios that the amount of theabove-mentioned cellulose ether is from 0.02 to 15, more preferably from0.1 to 10, most preferably from 0.15 to 8 percent, based on the weightof the powder. The foam can be contacted with a wide variety of powders.Any powder is useful which traditionally has been coated or agglomeratedwith a fluid. Preferred classes of useful powders are ingredients ofpharmaceutical granules or tablets, ingredients for granules or tabletsused in the food or agricultural industry, powders used in ceramicprocesses, or powdered detergents. It has been found that the foamlamellae generally break and reform as they pass through the powderduring granulation.

[0033] Advantageously the contact of the foam with the powder isconducted in a mixing device, such as a high shear mixing device, a lowshear mixing device, a fluidized bed granulator, a roller compactor or aspray dryer. The contact of the foam with powder can be carried out invarious ways.

[0034] According to one way of powder agglomeration, the mixing deviceis set into operation after the powder and the foam have been fed to themixing device. Preferably, the powder is fed to the mixing device, foamis placed on top of the powder and the mixing device is subsequently setinto operation. This method prevents dust emission during theagglomeration step. Surprisingly, is has been found that a uniformdispersion of the foam in the powder can be achieved within a very shortperiod after the mixing device has been set in operation, usually withinless than 30 seconds, in most cases even within less than 10 seconds,even when the entire amount of foam is placed on top of the powder andthe mixing device is set into operation only afterwards. This finding isin contrast to known processes wherein a corresponding liquidcomposition is directly dispersed in the powder without formation offoam from the fluid composition. If the liquid is added on top of thepowder, large lumps are formed and a uniform dispersion of the liquid inthe powder is impossible.

[0035] According to another way of powder agglomeration, powder and afoam portion are fed to a mixing device, the mixing device is set intooperation to disperse the foam portion in the powder, the operation ofthe mixing device is stopped, an additional foam portion is fed to themixing device, and the previous steps are repeated several times.

[0036] Alternatively, the powder is loaded into a mixing device and foamis added continuously or in portions to the mixing device while themixing device is in operation.

[0037] According to the described process of agglomerating powders asurprisingly homogeneous dispersion of the cellulose ether and optionalother foam components in the powder is achieved. Moreover, a simpledevice can be used for applying the foam to the powder, such as a simpletube. Maintenance-intensive, expensive and complex atomizing devicesthat are commonly used for spraying fine droplets of liquids on a powderin know agglomeration processes with liquids are not necessary. Thedispersion of the foam in the powder is achieved at a rate which iscomparable to or even faster than the dispersion of a correspondingliquid spray in the powder. The described method of agglomeratingpowders is also useful for dispersing poorly water-soluble compounds,such as poorly water-soluble drugs, in the powder.

[0038] The foam of the present invention is also useful for coatingsolid particles, such as tablets, granules, pellets, caplets, capsules,lozenges, suppositories, pessaries or implantable dosage forms. Theweight ratio between the foam and the solid particles generally is from1:20 to 1:0.002, preferably from 1:10 to 1:0.01, more preferably from1:5 to 1:0.1. Preferably, the foam and the solid particles are contactedin such ratios that the amount of the above-mentioned cellulose ether isfrom 0.01 to 20, more preferably from 0.05 to 15, most preferably from0.075 to 10 percent, based on the weight of the solid particles. Thesolid particles are preferably agitated, such as tumbled, dipped throughthe foam or otherwise moved during the coating. The agitation of theparticles can be started before, during or after the contact of theparticles with the foam. However, agitation of the particles ispreferably started before the foam is added to the particles and iscontinued during the foam addition. More preferably, foam is added tocontinuously agitated solid particles. The coating can be conducted in aknown coating device, for example in a tumbler, perforated side-ventedcoating pan, Wurster column insert in a fluid-bed device, low-shearblender or a continuous coating device of any configuration. Preferably,the foam is added continuously or semi-continuously to agitated solidparticles. The foam can be added to the solid particles by means of asimple tube of which the end is placed closely to or into the mass ofsolid particles. A surprisingly smooth coating of constant thickness onthe solid particles is achieved. Usually up to 5 coats, in most casesonly up to 3 coats, typically even 1 to 2 coats are sufficient toprovide a glossy, smooth coating of constant thickness and good gloss.

[0039] The present invention is further illustrated by the followingexamples which should not be construed to limit the scope of the presentinvention. All parts and percentages are by weight unless otherwiseindicated.

[0040] The alkyl and hydroxyalkyl substitutions of the cellulose ethersindicated in the examples below are measured and calculated according toASTM D3876.

[0041] The apparent viscosities indicated in the examples below aremeasured and normalized to a 2 weight percent aqueous solution using anUbbelohde viscometer at 20° C. The foam quality FQ is measured byfilling a container of 280 ml volume with foam at 25° C. and atmosphericpressure, centrifuging the foam to collapse it and measuring the volumeof the resulting liquid. The foam quality is measured according to thefollowing formula:

FQ(%)=[gas volume/(gas volume+fluid volume)×100].

EXAMPLES 1-3

[0042] In Example 1 an aqueous solution containing 1 weight percent of ahydroxypropyl methylcellulose described below is prepared.

[0043] In Example 2 an aqueous solution containing 1 weight percent of ahydroxypropyl methylcellulose described below and 0.001 weight percentof a sodium lauryl sulfate, a surfactant, is prepared.

[0044] In Example 3 an aqueous solution containing 5 weight percent of ahydroxypropyl methylcellulose described below is prepared.

[0045] The hydroxypropyl methylcellulose has a methoxyl substitution of28-30 percent, a hydroxypropoxyl substitution of 7-12 percent and aviscosity of about 6 mPa·s. The hydroxypropyl methylcellulose iscommercially available from The Dow Chemical Company under the TrademarkMETHOCEL E6PLV.

[0046] From the aqueous solution a foam is prepared as illustrated inFIG. 1. Air flows through a tube 31 equipped with ball valves 1, 2 and5, with pressure regulators and gauge 3 and 9, with a pressure reliefvalve 4, a mass flow controller 6, a pressure gauge 7 and a check valve8. The pressure in tube 31 is regulated to about 414 kPa. The aqueoussolution is passed from a pressure vessel 10, which is equipped with apressure relief valve 12, needle valve 11, air inlet tube 34 and adip-pipe 33, through a tube 32. The pressure in tube 32 is regulated toabout 414 kPa. Tube 32 is equipped with a ball valve 13, a needle valve14, an oval gear flow meter 15, a pressure gauge 16 and a check valve 17and with a water supply line 28, a ball-valve 29 and a check valve 30.The air stream and fluid stream meet in T-piece 18 comprising anair-inlet port 19, a fluid inlet port 20 and a foam outlet port 21. Theair stream is dispersed in the water stream by in-line filters 22 and 24and additionally in packed tube 23 whereby the foam is produced andexits the foam production device via tube 26 or 27 according to theposition of 3-way valve 25. The foam experiences a pressure of about 414kPa before it exits the foam production device. When it is released fromthe foam production device to the environment of atmospheric pressure,it expels excess air which manifests itself as pockets of air within thefoam. The formation of a mist is not observed in any of the examples.

[0047] The in-line filters used for preparing the foams in the exampleshave a pore size of 90 micrometers, but generally in-line filters withpore sizes of from 0.5 to 90 micrometers, more preferably from 15 to 90micrometers are useful for simple foams. For foams containing solids oremulsions, the in-line filters are preferably replaced with strainerelements whose only function is to keep the glass beads in tube 23. Suchstrainer elements preferably have a nominal pore size of about 440micrometers. The in-line filters 22 and 24 are connected via a tube 23.The stainless steel tube 23 in the foam production device used in theexamples is approximately 25 cm. long by 12.8 cm. external diameter, andis packed with glass beads of 3 mm diameter. Other packed-tube foamgenerators are described in detail in “A mechanical foam-generator foruse in laboratories”, by J. F. Fry and R. J. French, J. Appl. Chem., 1,425-429 (1951). The operation of the foam generating device is known tothe skilled artisan.

[0048] The properties of the foams produced according to Example 1 arelisted in Table 1 below.

[0049] In the following tables, “Foam Density⁵⁾” should be regarded as“Apparent Foam Density” due to the fact that foams are weighed in air.TABLE 1 liquid Foam Liquid Foam foam Foam air flow flow³⁾ FQ_(T) ¹⁾density²⁾ volume⁴⁾ volume⁴⁾ weight⁴⁾ density⁵⁾ (l/min.) (l/min.) (%)(g/ml) (ml) (ml) (g) (g/ml) FQ⁵⁾ 5.00 0.01 99.8 0.002 35 280 30.0 0.1188 5.00 0.05 99.0 0.010 30 280 19.5 0.07 89 5.00 0.10 98.0 0.019 25 28016.3 0.06 91 4.00 0.01 99.8 0.002 30 280 24.5 0.09 89 4.00 0.05 98.80.012 20 280 16.0 0.06 93 4.00 0.10 97.6 0.024 18 280 13.2 0.05 94 3.000.01 99.7 0.003 25 280 19.9 0.07 91 3.00 0.05 98.4 0.016 25 280 15.50.06 91 3.00 0.10 96.8 0.032 20 280 13.0 0.05 93 2.00 0.01 99.5 0.005 20280 17.1 0.06 93 2.00 0.05 97.6 0.024 15 280 11.1 0.04 95 2.00 0.10 95.20.048 20 280 14.3 0.05 93

[0050] The properties of the foams produced according to Example 2 arelisted in Table 2 below. TABLE 2 liquid Foam Liquid Foam foam Foam airflow flow³⁾ FQ_(T) ¹⁾ density²⁾ volume⁴⁾ volume⁴⁾ weight⁴⁾ density⁵⁾(l/min.) (l/min.) (%) (g/ml) (ml) (ml) (g) (g/ml) FQ⁵⁾ 5.00 0.01 99.80.002 25 280 30.0 0.11 91 5.00 0.05 99.0 0.010 20 280 19.5 0.07 93 5.000.10 98.0 0.019 20 280 16.3 0.06 93 2.00 0.01 99.5 0.005 20 280 24.50.09 93 2.00 0.05 97.6 0.024 20 280 16.0 0.06 93 2.00 0.10 95.2 0.048 20280 13.2 0.05 93

[0051] The properties of the foams produced according to Example 3 arelisted in Table 1 below. TABLE 3 liquid Foam Liquid Foam foam Foam airflow flow³⁾ FQ_(T) ¹⁾ density²⁾ volume⁴⁾ volume⁴⁾ weight⁴⁾ density⁵⁾(l/min.) (l/min.) (%) (g/ml) (ml) (ml) (g) (g/ml) FQ⁵⁾ 5.00 0.01 99.80.002 75 280 70.0 0.25 73 5.00 0.05 99.0 0.010 85 280 69.2 0.25 70 5.000.10 98.0 0.020 75 280 66.3 0.24 73 4.00 0.01 99.8 0.002 75 280 70.30.25 73 4.00 0.05 98.8 0.012 75 280 69.6 0.25 73 4.00 0.10 97.6 0.025 70280 66.4 0.24 75 3.00 0.01 99.7 0.003 90 280 71.7 0.26 68 3.00 0.05 98.40.016 90 280 69.8 0.25 68 3.00 0.10 96.8 0.033 90 280 84.9 0.30 68 2.000.01 99.5 0.005 85 280 74.6 0.27 70 2.00 0.05 97.6 0.025 80 280 80.10.29 71 2.00 0.10 95.2 0.049 90 280 85.9 0.31 68

Example 4

[0052] Examples 1-3 are repeated except that an aqueous solutioncontaining 2 weight percent of the above-described hydroxypropylmethylcellulose, commercially available from The Dow Chemical Companyunder the Trademark METHOCEL E6PLV is prepared. The solution is coloredwith a green food dye for increased visibility. Foam is produced as inExamples 1-3. The air flow is 5.0 l/min. The liquid flow is 0.1 l/min.The theoretical foam quality FQ_(T) is 98.0%. FIG. 2 represents aphotograph of the foam flowing through a tube of a foam-generatingdevice. Air-foam boundaries are visible, which indicates that pockets offoam are interspersed with pockets of air. In FIG. 2 the pockets of airflowing through the tube are marked with arrows.

1. An aqueous air foam comprising a non-crosslinked cellulose etherselected from the grout consisting of C₁-C₃-alkyl celluloses,C₁-C₃-alkyl hydroxy-C₁₋₃-alkyl celluloses, hydroxy-C₁₋₃-alkyl cellulosesand mixed hydroxy-C₁-C₃-alkyl celluloses, the foam having a foam qualityFQ of from 60 to 97 percent and the foam quality being defined asFQ(%)=[air volume/(air volume+fluid volume)×100].
 2. The foam of claim 1wherein pockets of aqueous air foam are interspersed with pockets ofair.
 3. The foam of claim 1 comprising a methyl cellulose or ahydroxypropyl methyl cellulose.
 4. The foam of claim 1 wherein theaqueous air foam comprises from 0.01 to 30 weight percent of thecellulose ether, based on the total weight of the cellulose ether andwater.
 5. The foam of claim 1 comprising no surfactant other than thecellulose ether.
 6. The foam of claim 1 having a foam quality FQ of from65 to 95 percent.
 7. A process for agglomerating solid particles whereinan aqueous air foam is contacted with solid particles to beagglomerated, the aqueous air foam comprising a non-crosslinkedcellulose ether selected from the group consisting of C₁-C₃-alkylcelluloses, C₁-C₃-alkyl hydroxy-C₁₋₃-alkyl celluloses,hydroxy-C₁₋₃-alkyl celluloses and mixed hydroxy-C₁-C₃-alkyl cellulosesthe foam having a foam quality FQ of from 60 to 97 percent and the foamquality being defined as FQ(%)=[air volume/(air volume+fluidvolume)×100].
 8. The process of claim 7 wherein a powder isagglomerated.
 9. A process for coating solid particles wherein anaqueous air foam is contacted with the solid particles to be coated, theaqueous air foam comprising a non-crosslinked cellulose ether selectedfrom the group consisting of C₁-C₃-alkyl celluloses, C₁-C₃-alkylhydroxy-C₁₋₃-alkyl celluloses hydroxy-C₁₋₃-alkyl celluloses and mixedhydroxy-C₁-C₃-alkyl celluloses, the foam having a foam quality FQ offrom 60 to 97 percent and the foam quality being defined as FQ(%)=[airvolume/(air volume+fluid volume)×100].
 10. The process of claim 9wherein tablets, granules, pellets, caplets, capsules, lozenges,suppositories, pessaries or implantable dosage forms are coated.
 11. Thefoam of claim 3 wherein the aqueous air foam comprises from 0.01 to 30weight percent of the cellulose ether, based on the total weight of thecellulose ether and water.
 12. The foam of claim 11 having a foamquality FQ of from 65 to 95 percent.
 13. The process of claim 7 whereinthe foam comprises a methyl cellulose or a hydroxypropyl methylcellulose.
 14. The process of claim 13 wherein the aqueous air foamcomprises from 0.01 to 30 weight percent of the cellulose ether, basedon the total weight of the cellulose ether and water.
 15. The process ofclaim 14 wherein the foam has a foam quality FQ of from 65 to 95percent.
 16. The process of claim 15 wherein a powder is agglomerated.17. The process of claim 9 wherein the foam comprises a methyl celluloseor a hydroxypropyl methyl cellulose.
 18. The process of claim 17 whereinthe aqueous air foam comprises from 0.01 to 30 weight percent of thecellulose ether, based on the total weight of the cellulose ether andwater.
 19. The process of claim 18 wherein the foam has a foam qualityFQ of from 65 to 95 percent.
 20. The process of claim 19 whereintablets, granules, pellets, caplets, capsules, lozenges, suppositories,pessaries or implantable dosage forms are coated.